I may have just found my answer buried in another thread. If this is correct, sorry, I search my head off before I post a new thread..
Air pump? - when engine is cold - what is it?
Since I did my exhaust with the addition of ELH, up pipe, and catless devorced DP I have noticed some different sounds. I am trying to decipher between the "new" sounds of the exhaust and what the engine is doing. I have noticed when I start my car when it is cold in the morning or after work there is some sort of air pressure/fan noise that turns on for ~15 seconds (it may be the air pump for that matter, I know the 2012 WRX has one). Under this condition for the first 15 seconds, I can hear a gurgling popping noise in the exhaust like small backfires which sparked my questions. What actually is it (if its not the air pump)? What does it do? Does it ever come on except for cold starts?
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I just installed my EL Headers and i'm getting the same noise on cold starts. From what I hear on other vids it seems to be normal. Not sure what it is but it only happens when the air pump is on.
Remove the air pump and it will go away 
Since I am catless, there is no reason for an air pump any more, correct? Just another thing I have to add to the list of crap! I think this throws a CEL, will the AP adjust for this or is a tuner required?
There's no reason for the pump no matter what, IMO. Its sole purpose is to increase the ratio of good/bad coming out of the car. It's not like without it you're creating less bad emissions. The geniuses at the EPA came up with this ratio rule and the work around is to pump more 'good' air out with the bad at startup when bad emissions are at the worst. Bump the good and the ratio is happy. It makes no freakin sense!
Upon removal the atmospheric sensor needs to stay and the AP can turn off the CELs that com on.
Upon removal the atmospheric sensor needs to stay and the AP can turn off the CELs that com on.
PM incoming my friend. And no, that makes no sense in terms of helping the environment.
I bet it is a way to get around EPA emissions standards for cold starts. Some gasses are measured by parts per million (PPM), some are measured by percentage. The "exhaust sniffer" does not take all of the exhaust gasses into consideration, only a small sample; hence, increasing the number of particles flowing through the exhaust system would reduce the ratio of toxic gasses I.E. PPM or the %. I believe NOx is measured PPM and CO is measured as a percentage.
Anyway... I'm catless now so they can suck it :devil:
I bet it is a way to get around EPA emissions standards for cold starts. Some gasses are measured by parts per million (PPM), some are measured by percentage. The "exhaust sniffer" does not take all of the exhaust gasses into consideration, only a small sample; hence, increasing the number of particles flowing through the exhaust system would reduce the ratio of toxic gasses I.E. PPM or the %. I believe NOx is measured PPM and CO is measured as a percentage.
Anyway... I'm catless now so they can suck it :devil:
I used to do some work with the EPA. What a fuckin disaster :lol:
^That makes my day
Blind leading the blind??
Blind leading the blind??
^^^ the EPA = "Revenge of the 'C' students"
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